Simple steps to install ETS2 Mods:

- download the mod «Volvo FH 2009 v18.3r by Pendragon»
- use WinRAR or 7-zip and unzip the archive;
- copy the file with the extension .scs in My Documents/Euro Truck Simulator/mod folder
- start the game, go to your profile, see the Mod manager and activate the mod.